Vehicles may be fitted with evaporative emission control (EVAP) systems to reduce the release of fuel vapors to the atmosphere. For example, vaporized hydrocarbons (HCs) from a fuel tank may be stored in a fuel vapor canister packed with an adsorbent which adsorbs and stores the fuel vapors. At a later time, when the engine is in operation, the evaporative emission control system allows the fuel vapors to be purged into the engine intake manifold from the fuel vapor canister. The fuel vapors are then consumed during combustion. Quick connectors (also called quick connects or snap fit connectors) may be used to couple the various fluid-carrying conduits and components (such as valves) of the EVAP system. The connectors may be shaped and structured to be closed in a single uniaxial movement which facilitates automated assembly as well as part servicing. In addition, the simple design of the connector makes it inexpensive to manufacture.
During certain conditions, the EVAP system may be monitored to identify breaches that can result in unwanted fuel vapor leaks. As an example, leaks can occur at the interfaces of the various conduits and valves of the EVAP system, such as at the locations where the quick connectors are coupled to the conduits and valves. One example approach for verifying EVAP system integrity includes application of negative pressure to the EVAP system and monitoring a subsequent rise in pressure. The presence of a leak, such as due to disconnection of a connector, may be inferred based on a faster than expected rise in pressure following the application of negative pressure. Another example approach for verifying that a quick connect is latched is shown by Beans in U.S. Pat. No. 6,113,151. Therein, following attachment of a connector to a fluid conduit, a sealing interface between the conduit and the connector is tested by application of a positive pressure from a high pressure source.
However, the inventors herein have recognized potential issues with such systems. As one example, there may be situations where the connector remains unlatched and a leak test is passed. For example, leaks may occur in the EVAP and fuel system (herein together termed fuel vapor system) due to the connector being snapped in but not locked. If the connector is inserted but not locked, the connector may seal momentarily and pass the leak test when the negative pressure is applied since the testing is done in static vehicle conditions while a vehicle engine is idling. However, when the vehicle goes on the road, vibration and surface feedback can cause the connector to pop open. The need for a dedicated pressure source for detection of an unlatched connector adds component cost and complexity. Further, the negative pressure from a vacuum-based leak test may pull in the connector and maintain the loose seal unlatched despite the leak test being passed. As such, this can result in earlier than expected warranty issues for the EVAP system. In addition, the vehicle may be emissions non-compliant.
In one example, the issues described above may be addressed by a method for detecting unlatching of a fuel vapor line connector, comprising: reverse rotating an engine unfueled while opening a purge valve to apply positive pressure from an intake manifold on a fuel vapor system; and indicating disconnection of a connector coupled to a fuel vapor conduit of the fuel vapor system based on a pressure response following the application of positive pressure. The application of positive pressure to the fuel vapor system is followed by monitoring pressure in the system. An unexpected drop in the positive pressure may indicate a quick connector disconnection or other leak in the system. The positive pressure test may be following by an application of negative pressure, and the quick connector disconnection may be confirmed based on the pressure response following the application of negative pressure. In this way, leaks in a fuel vapor system due to unlatching of a connector can be identified more accurately and addressed in a timely manner.
As one example, at an assembly facility or a service station, a service tool may be coupled to a vehicle and the vehicle may be shifted to service mode. Positive pressure generated at the engine may then be applied to the fuel vapor system of the vehicle to detect unlatching of any quick connectors coupled to different conduits and components of the fuel vapor system. The positive pressure unlatches any quick connectors that may have been loosely attached, but not locked in place. A faster/higher than expected drop in intake manifold pressure is used to infer the presence of a leak in the fuel vapor system generated by the disconnection or un-latching of a quick connector. Un-latching of quick connectors may cause large leaks in the fuel vapor system which may take only a few seconds to be detected by application and monitoring of positive pressure. The positive pressure applied for the leak test may be generated by spinning the vehicle engine, unfueled, in reverse (opposite to the direction of engine rotation during normal vehicle operation), using an electric machine, such as an electric motor. Alternatively, a fuel tank pump may be operated to warm up and agitate fuel, thereby generating positive fuel vapor pressure. Further still, positive pressure may be generated by operating an electric pump of the engine leak detection system through a reversing circuit. Following the positive pressure test, a negative pressure leak test may also be carried out to confirm the presence of any leaks and unlatched connectors.
In this way, actual and imminent leaks caused by quick connector unlatching in a fuel vapor system may be detected at the end of an assembly line and/or at a service station. The technical effect of diagnosing for leaks by sequentially applying positive pressure followed by negative pressure is that false negative leak results can be reduced. In particular, the technical effect of applying positive pressure to the fuel vapor system first is that loosely attached quick connectors may be fully unlatched, exposing any imminent leaks. As such, loosely attached connectors that may have passed the negative pressure test (due to the vacuum pulling the unlatched connector closer to the conduit) may be fully unlatched due to the positive pressure, ensuring the detection of a leak. By using positive pressure for the leak test generated via the reverse rotation of an unfueled engine, or via the operation of an existing system pump, such as a fuel pump, the need for a dedicated pressure source is reduced, providing component and cost reduction benefits. By improving the diagnostics for loosely fitted quick connectors, system integrity can be ensured and emissions compliance may be improved. In addition, early warranty issues for the EVAP system may be avoided.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.